1. Field of the Invention
The invention relates to a mixture containing a monophosphite ligand and the use thereof for catalysis of a hydroformylation reaction.
2. Discussion of the Background
The reactions between olefin compounds, carbon monoxide and hydrogen in the presence of a catalyst to give the aldehydes comprising one additional carbon atom are known as hydroformylation or oxo synthesis. The catalysts used in these reactions are frequently compounds of the transition metals of group VIII of the Periodic Table of the Elements. Known ligands are, for example, compounds from the classes of the phosphines, phosphites and phosphonites, each with trivalent phosphorus PIII. A good overview of the state of the hydroformylation of olefins can be found in B. CORNILS, W. A. HERRMANN, “Applied Homogeneous Catalysis with Organometallic Compounds”, vol. 1 & 2, VCH, Weinheim, New York, 1996 or R. Franke, D. Selent, A. Börner, “Applied Hydroformylation”, Chem. Rev., 2012, DOI:10.1021/cr3001803.
The type of catalyst system and the optimal reaction conditions for the hydroformylation are dependent on the reactivity of the olefin used.
The different reactivity of isomeric octenes is likewise known (see B. L. Haymore, A. van Hassell, R. Beck, Annals of the New York Acad. Sci., 415, 1983, p. 159-175).
Via the different processes and catalysts, a multitude of olefins are available for the hydroformylation (see P. W. N. M. van Leeuwen, in Rhodium Catalyzed Hydroformylation, P. W. N. M. van Leeuwen, C. Claver (eds.), Kluwer, Dordrecht, 2000).
Technical olefin mixtures which are used as reactants for the oxo process often contain olefins of a wide variety of different structures, having different levels of branching, different double bond positions in the molecule and possibly also different carbon numbers. This is particularly true of olefin mixtures which have formed through di-, tri- or substantial oligomerization of olefins. Examples of technical olefin mixtures which are converted to the corresponding aldehyde mixtures by hydroformylation include tri- and tetrapropene, and di-, tri- and tetrabutene.
The abovementioned technical olefin mixtures often contain only small proportions of olefins having terminal double bonds. In order to prepare products in which more terminally hydroformylated aldehyde is present than in the original olefin mixture therefrom, it is necessary to hydroformylate under isomerizing conditions.
Suitable processes for this purpose are, for example, high-pressure hydroformylations with cobalt catalysts. However, disadvantages of these processes include the fact that a relatively large number of by-products such as alkanes, acetals and ethers are formed and that very severe reaction conditions (high temperature, high pressure) are necessary (see also Klaus-Diether Wiese, Dietmar Obst, Top. Organomet. Chem. 2006, 18, 1-33).
When rhodium complexes are used as catalyst, the ligand is another crucial factor for the product composition of the aldehydes. Unmodified rhodium-carbonyl complexes catalyse the hydroformylation of olefins having terminal and internal double bonds, where the olefins may also be branched, to give aldehydes having a high level of branching. The proportion of terminally hydroformylated olefin is much lower compared to the cobalt-catalysed product.
The hydroformylation of olefins having internal double bonds over catalyst systems containing sterically demanding bisphosphite ligands proceeds with good selectivity in the case of long-chain olefins, but with an unsatisfactory activity (P. W. N. M. van Leeuwen, in Rhodium Catalyzed Hydroformylation, P. W. N. M. van Leeuwen, C. Claver (eds.), Kluwer, Dordrecht, 2000).
In Angew. Chem. Int. Ed. 2000, 39, No. 9, p. 1639-1641 by Börner et al., phosphonites are used in hydroformylation, i.e. ligands having one P—C and two P—O bonds. The phosphonites described here, when used in hydroformylation, have n/iso selectivity (n/iso=the ratio of linear aldehyde (=n) to branched (=iso) aldehyde)) of 0.61 to 1.57.
However, the preparation of these ligands based on a phosphorite structure, in the case of an industrial-scale synthesis, is much more complex than, for example, the preparation of phosphite ligands. This point is a crucial factor especially in the case of use of these ligands in an industrial scale process. The synthesis of the compounds used as ligands should be as inexpensive and simple as possible.
Rhodium-monophosphite complexes in catalytically active compositions, in contrast, are suitable for the hydroformylation of branched olefins having internal double bonds.
Since the 1970s, there have been descriptions of the use of “bulky phosphites” in hydroformylation (see, inter alia, van Leeuwen et al., Journal of Catalysis, 2013, 298, 198-205). These feature good activity, but the n/i selectivity for terminally hydroformylated compounds is in need of improvement.
As well as the use of pure ligands, the use of ligand mixtures has also been described in the literature.
US 20120253080 describes the use of monophosphites with bisphosphites. However, this combination has the disadvantage that the bisphosphites, although having good selectivity, have very low activity in the case of long-chain olefins and are therefore in need of improvement. In an industrial scale process, in addition to the selectivity for the desired product, the space-time yield or the activity of the catalyst system is also an important factor with regard to the economic viability thereof. Moreover, the bisphosphites are frequently much more costly to prepare than, for example, monophosphites.
EP 1 099 678 describes the use of phosphonites with bisphosphites. However, it is disadvantageous here that both ligand types are very costly to produce, and an industrial scale process can therefore hardly be economically viable. Moreover, the addition of the bisphosphite ligand noticeably affects the yield of the reaction, since these ligands are less active when dibutene, for example, is used as substrate.
It is therefore desirable to develop a catalyst system which does not have the disadvantages exhibited in the related art.